The present invention concerns magnetic bubble memory devices, and more particularly it concerns magnetic bubble memory devices wherein the intensity of the rotating magnetic field is amplified without increasing the amplitude of the current for generating the rotating magnetic field.
Generally, a magnetic bubble memory device comprises a magnetic thin film formed on a non-magnetic substrate such as made of garnet by liquid phase epitaxial growth process or the like, a magnetic bubble memory chip comprising soft ferromagnetic material formed on the magnetic thin film and a pattern made of conductive material, an insulating substrate to carry the chip, signal transmission leads to electrically connect the chip and an external circuit, X and Y coils to generate a rotating magnetic field which is parallel to the major surface of the chip, and a permanent magnet to generate a bias magnetic field which is vertical to the major surface of the chip. The device writes in, memorizes and reads out the desired information by causing the magnetic bubbles to generate, propagate and replicate in the thin film pattern comprising the soft ferromagnetic material.
However, there were major problems to be solved, as listed below, in the conventional art for providing a compact and large capacity magnetic bubble memory device constructed as above at low prices, and these problems hindered the practical materialization of the device.
(1) Miniaturization of coils for rotating magnetic field: PA0 (2) Minimization of voltage-current (VI) product in coils for rotating magnetic field: PA0 (3) Minimization of power consumption: PA0 (4) As for bias magnetic field margin indicating operational characteristics of a magnetic bubble memory device (the range of bias magnetic field in which the device can operate stably), the bias magnetic field margin becomes wider as the intensity of the rotating magnetic field increases, and as the diameter of the magnetic bubble becomes smaller, the level of the margin becomes higher and shifts toward the direction in which the rotating magnetic field intensity increases. Therefore, if the bubble diameter is decreased to make the magnetic bubble memory device more compact and increase its capacity, then a large rotating magnetic field is required in order to operate the magnetic bubble memory device stably. For this purpose, the amplitude of the current supplied to X, Y coils must be increased, which fact contradicts the points raised above in (2) and (3). PA0 (5) Magnetic field intensity in the direction of X within X coil, and that in the direction of Y within Y coil respectively become maximum at the center of the lengths of X, Y coils, and decrease toward the opposite end openings of the coils. For this reason, the level of the maximum value at the center rises if it is intended to obtain a sufficient intensity of magnetic field at the opposite ends, which in turn increases the power consumed at X, Y coils and raises the temperature in the chip.
In order to obtain a compact magnetic bubble memory device, it is necessary to miniaturize X, Y coils for rotating magnetic field.
When a current of more than 100 KHz is supplied to X, Y coils for rotating magnetic field, terminal voltage at X, Y coils become excessive, thereby causing problems concerning allowable voltage for transistors for the driving circuit. In this case, it is desirable to avoid using transistors with a high allowable voltage but use inexpensive integrated circuits (IC) for driving purposes.
Generally speaking, performance characteristics of magnetic bubble memory devices as such that they are dependant on temperature; when the temperature in the chip rises, the operation margin becomes smaller. Accordingly, it is necessary to decrease the power consumption at X, Y coils which greatly take part in the generation of heat.
As explained above, in the conventional type magnetic bubble memory device, the amplitude of the current for generating the rotating magnetic field must be increased in order to increase the intensity of the rotating magnetic field, which in turn increases the power consumption at X, Y coils, raises the chip temperature, and deteriorates the operation margin.